Reaction formula

Reagents

Step-by-step instruction

WARNING! This experiment is dangerous! You should NOT
perform this at home. ONLY carry out this experiment, if
you are a trained chemist, and you understand local
safety and legal requirements, which are required to
perform such experiments

I am aware of legal and safety requirements needed to
conduct this experiment

There are a few ways to obtain hydrogen sulfide in the laboratory. Let’s consider the most common two.

The first of them is heating of sulfur/paraffin mixture. Place a piece of paraffin into the test- tube. Add some powdered sulfur. Clamp the test-tube on a stand. Fix it at an angle about 45o. Seal the test-tube with a stopper with a gas delivery tube. Heat the test tube gently. The released hydrogen sulfide could be detected by wet universal indicator paper. It turns red under action of hydrogen sulfide.

The other way to synthesize hydrogen sulfide is the reaction between diluted hydrochloric (or sulfuric) acid and zinc or iron sulfide. Put some zinc sulfide to the flask. Fix up the thistle funnel and gas delivery tube at the flask mouth. Fill the thistle funnel with hydrochloric acid. Add some acid using the thistle funnel. Hydrogen sulfide is released.

To test hydrogen sulfide gas properties prepare hydrogen sulfide water. Put the end of the gas delivery tube connected with a source of hydrogen sulfide to the beaker with cold water. Bubble the gas through the water for a while. Hydrogen sulfide is partially dissolved producing hydrogen sulfide water.

Divide the obtained hydrogen sulfide water between two test tubes.

Add a few drops of litmus indicator to the first test tube. The solution turns red.

Add some copper sulfate solution to the second test tube. The formation of a black precipitate is observed.

Scientific background

Hydrogen sulfide is a colorless gas with a characteristic smell resembling rotten eggs. At high concentrations it is toxic. Paraffin and sulfur react under heating producing hydrogen sulfide and carbon. This reaction is more convenient compared to the reaction of sulfides with diluted acid since it allows controlling the gas flow precisely. Addition of diluted acid to iron or zinc sulfide also leads to release of hydrogen sulfide in a double exchange reaction.

The solution of hydrogen sulfide in water is a very weak acid. That is why acid base indicators change their color according to pH shift. For example litmus turns red in solution of hydrogen sulfide. The reaction of hydrogen sulfide water with copper sulfate is analogous to the well-known qualitative reaction on hydrogen sulfide with lead ions. Just as lead, copper sulfate forms an insoluble black precipitate of copper sulfide.

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